As one method for increasing an operation speed of a MOSFET, there may be mentioned a method in which a silicon crystal in a channel region is distorted to improve the mobility of carriers. For example, when SiGe is buried in a source and a drain region of a pMOSFET, a compressive stress may be applied to a channel region. As a result, the mobility of holes may be increased.
On the other hand, when SiGe is buried in a source and a drain region of an nMOSFET, the performance thereof is degraded. Hence, it is preferable that SiGe be buried in a source and a drain region of a pMOSFET and not be buried in a source and a drain region of an nMOSFET.
When gate electrodes of a plurality of pMOSFETs are disposed in one active region at a high density, it becomes difficult to bury SiGe in a source and a drain region of each pMOSFET without burying SiGe in a source and a drain region of each nMOSFET.